Serpentine accessory drive systems are routinely used in automotive vehicles to drive engine accessories. A typical serpentine drive system includes a driving pulley on the crankshaft of an internal combustion engine of the vehicle, a series of driven pulleys for the accessories and a multi-ribbed belt trained about the driving and driven pulleys. An advantage of the serpentine drive is that, by providing an automatic belt tensioner on the belt, the accessories can be fixedly mounted.
The driving pulley establishes a highly dynamic loading on the belt. This high dynamic loading is due to the variable torque output characteristics of internal combustion engines. Under this circumstance, the tensioner cannot accommodate all of the variable torque characteristics and belt load changes caused by the variable torque. The result can be noise and decreased belt life due to instantaneous belt slippage.
Representative of the art is U.S. Pat. No. 6,083,130 (2000) which discloses a serpentine belt drive system for an automotive vehicle comprising a drive assembly including an internal combustion engine having an output shaft with a driving pulley thereon rotatable about a driving pulley axis. A sequence of driven assemblies each has a driven pulley rotatable about an axis parallel with the driving pulley axis and a serpentine belt mounted in cooperating relation with the driving pulley and with the driven pulleys in a sequence which corresponds with the sequence of the driven assemblies when related to the direction of movement of the belt to cause said driven pulleys to rotate in response to the rotation of the driving pulley. The sequence of driven assemblies includes an alternator assembly including an alternator shaft mounted for rotation about a shaft axis. A hub structure is fixedly carried by the alternator shaft for rotation therewith about the shaft axis. A spring and one-way clutch mechanism couples the alternator pulley with the hub structure. The spring and one-way clutch mechanism comprises a resilient spring member separately formed from and connected in series with a one-way clutch member. The resilient spring member is constructed and arranged to transmit the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the alternator shaft is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient movements in opposite directions with respect to the alternator pulley during the driven rotational movement thereof. The one-way clutch member is constructed and arranged to allow the hub structure and hence the alternator shaft to rotate at a speed in excess of the rotational speed of the alternator pulley when the speed of the engine output shaft is decelerated to an extent sufficient to establish the torque between the alternator pulley and the hub structure at a predetermined negative level.
What is needed is an isolator decoupler comprising a torsion spring engaged between the pulley and the one-way clutch to resiliently couple the pulley to the shaft, and the pulley non-resiliently directly coupleable to the shaft in a temporary predetermined loaded condition. The present invention meets this need.